Can you backflush it?

On my yamaha, when I disconnect the pee hose from the nipple on the lower cowling, the diameter of the pee hose is about 1/4 inch. On my garden hose, I have a multi-function nozzle. The pee hose fits over the sharp stream nipple on the garden hose nozzle. I can hold the peehose over the nipple and backflush the cooling passages.

The thermostat should have no effect on the telltale.

My motor does not pee on startup at the lowest idle speed. Raise the idle and it pees.

You won't damage the impeller in seven seconds if it is wet and otherwise sound. Running dry is what does them in.

Hope this helps.